Acarine colonisation of Antarctica and the islands of the Southern Ocean: the role of zoohoria

A quarter of the terrestrial Acari recorded from Antarctica and the sub-Antarctic islands are parasitic haematophages or non-feeding phoretics associated with other larger and more mobile animals, especially sea birds and pterygote insects. Although flying sea birds are effective vectors of zoohoric mites into the region, penguins are not and merely serve as reservoir hosts. Similarly, most of the mites associated with insects were accidentally introduced by man as free-living adults that subsequently utilised a range of alien and indigenous insects as local dispersal mechanisms

Non-indigenous Acari of Antarctica and the sub-Antarctic islands

Approximately 70 species out of a total of more than 520 Acari recorded from Antarctica and the sub-Antarctic islands may originate from other continents, especially Australasia, South America and Europe. Although some species have probably been carried into the region on migrant birds, most may have been introduced as a result of human activity, in particular by whalers and sealers. The majority of species appear to originate from imported sheep, rabbits, rats and fowl, and a few from vegetation, soil and ship's stores

The structure and function of the tarsus I sensillar field in mites of the genusHalarachne(Halarachnidae: Gamasida)

The sensillar field on tarsus I of Halarachne (Halarachnidae: Gamasida), a respiratory tract endoparasite of seals (Pinnipedia) is associated with 12 hair- or peg-like receptor sensilla in the larva and 13 or 14 in the adult. These include thermo-hygroreceptors, each with a double wall traversed by 3 or 4 slit-like pores (dw/WP-sensilla), olfactory chemoreceptors of small inorganic molecules, each with a single wall spanned by several small and simple pores (sw/WP-sensilla), gustatory chemoreceptors with a single terminal pore (TP-sensilla), and aporous NP-sensilla which have thermoreceptive and/or other unknown functions. Some sensilla are sessile and others socketed, the latter having a possible additional/alternative mechanoreceptive function. One mechanoreceptor is a probable trichobothrium-like vibration receptor which has not been previously described in the Anactinotrichida. This range of sensilla combined with the absence of sw/WP-sensilla, i.e. olfactory chemoreceptors covered with numerous, large centrally-plugged pores, suggests that although Halarachne spp. can locate large endothermic animals, they lack the ability to discriminate between different species

Supercooling points and water content in Acari

Supercooling point is correlated with total body water content in a wide range of terrestrial Acari from Antarctic, sub-Antarctic and temperate regions, which have not been cold-hardened by prior exposure to winter low temperatures. This suggests that low water content is itself an important pre-adaptive features conferring considerable cold-hardiness among terrestrial mites. Other physical and behavioural adaptations, for example clearing the gut of potential ice nucleating agents, accumulation of cryoprotectants and behavioural avoidance of low temperatures are considered to be possible secondary adaptations

Edaphic oribatid mites (Cryptostigmata: Acarina) associated with an aquatic moss on sub-Antarctic South Georgia

The moss Drepanocladus uncinatus (Hedw.) Warnst., from coastal freshwater habitats on the sub-Antarctic island of South Georgia harbours two species of hemi-edaphic oribatid mite namely Edwardzetes elongatus Wallwork (Ceratozetidae) and Trimaloconothrus flagelliformis Wallwork (Malaconothridae). Both mites feed upon microbiota and tolerate prolonged submersion in freshwater and their survival among the aquatic moss is a result of their pre-adaptation to similar conditions in flooded soil and vegetation, an absence of predators and minimal competition from other aquatic invertebrates. Freshwater habitats on sub-Antarctic islands are relatively young so that, in the future, terrestrial mites may eventually become displaced by more specialist aquatic macrofaunal colonists

Ecology of the littoral Halacaridae (Acari: Prostigmata) of South Georgia in the sub-Antarctic

Nine species of marine littoral Halacaridae were collected from Husvik Harbour, South Georgia, all of which are new to the fauna of the island. These include Isobactrus microdens Newell, Rhombognathus auster Bartsch, R. multisetosus Newell, R. plumifer Trouessart, Agauopsis inflatus Newell, Halacarellus novellus Bartsch and Pugh, H. porellus Bartsch and Pugh, Lohmannella bihamata Viets and L. grandipora Newell. The halacarid fauna is similar to that of southern South America, though depauperate and dominated by a single species, R. auster , which was found in large numbers and at all levels of the littoral zone. Low diversity probably results from isolation and/or severe climatic factors. Isolation includes both that of suitable habitable shores and the remoteness of South Georgia itself. The main climatic limitation is exposure to freezing air and icing during winter non-submergent neap tides

The Acari of fresh- and brackish water habitats in the Antarctic and sub-Antarctic regions

Neither the benthic Halacaroidea nor nektonic Hydrachnidia, characteristic of temperate and tropical freshwater mite faunas are represented among the twenty four species and sub-species of Acari recorded from the Antarctic and sub-Antarctic. The mites collected from the streams, lakes or brackish/freshwater pools of the region are either terrestrial species blown by wind into freshwater or interlopers from the marine littoral which have invaded coastal brackish pools. The present study reports on new collections of mites obtained from lakes and pools at a number of locations from both Continental and Maritime Antarctica, as well as from several sub-Antarctic islands. It reviews all published records for the region and the combined ‘fauna’ is then compared with that of temperate and tropical regions